PTHREAD_BARRIER(3) | Library Functions Manual | PTHREAD_BARRIER(3)

# NAME

pthread_barrier — barrier interface

# LIBRARY

POSIX Threads Library (libpthread, -lpthread)

# SYNOPSIS

#include <pthread.h>

int
pthread_barrier_init(pthread_barrier_t * restrict barrier, const pthread_barrierattr_t * restrict attr, unsigned int count);

int
pthread_barrier_destroy(pthread_barrier_t *barrier);

int
pthread_barrier_wait(pthread_barrier_t *barrier);

# DESCRIPTION

The pthread_barrier_init() function creates a new barrier with attributes attr and count. The count parameter indicates the number of threads which will participate in the barrier. The pthread_barrierattr_init(3) function may be used to specify the attributes supplied in attr. If attr is NULL, the default attributes are used. Barriers are most commonly used in the decomposition of parallel loops.

The pthread_barrier_destroy() function causes the resources allocated to barrier to be released. No threads should be blocked on barrier.

The pthread_barrier_wait() function causes the current thread to wait on the barrier specified. Once as many threads as specified by the count parameter to the corresponding pthread_barrier_init() call have called pthread_barrier_wait(), all threads will wake up, return from their respective pthread_barrier_wait() calls and continue execution.

# RETURN VALUES

If successful, pthread_barrier_init() will return zero and put the new barrier id into barrier, otherwise an error number will be returned to indicate the error.

If successful, pthread_barrier_destroy() will return zero. Otherwise an error value will be returned.

If successful, pthread_barrier_wait() will return zero for all waiting threads except for one. One thread will receive status PTHREAD_BARRIER_SERIAL_THREAD, which is intended to indicate that this thread may be used to update shared data. It is the responsibility of this thread to insure the visibility and atomicity of any updates to shared data with respect to the other threads participating in the barrier. In the case of failure, an error value will be returned.

# ERRORS

The pthread_barrier_init() function may fail if:

[EINVAL]
  The value specified by count is zero or attr is invalid.

The pthread_barrier_destroy() function may fail if:

[EBUSY]
  The barrier still has active threads associated with it.
[EINVAL]
  The value specified by barrier is invalid.

The pthread_barrier_wait() function may fail if:

[EINVAL]
  The value specified by barrier is invalid.

# SEE ALSO

pthread_barrierattr(3), pthread_cond(3), pthread_mutex(3)

# STANDARDS

These functions conform to IEEE Std 1003.1-2001 (“POSIX.1”).

July 8, 2010 | NetBSD 7.2